Jury selection began yesterday in the trial of Bernard C. Welch, the accused murderer of Dr. Michael Halberstam, after Superior Court Chief Judge H. Carl Moultrie I denied motions to delay the case because of the shooting of President Reagan and to move the trial to another jurisdiction.

Moultrie did, however, grant a request by defense attorney Sol Z. Rosen to sequester the jury to insulate its members from potential adverse publicity in the celebrated case.

In making his rulings, Moultrie said that Welch "cannot now complain that the very fact of publicity he sought interferes with his right to a fair trail."

Moultrie was apparently referring to interviews that Welch has voluntarily granted since his arrest. These include a controversial interview with Life magazine, for which the magazine paid Welch $8,000 to secure rights to a number of photographs accompanying an article based on the interview, as well as subsequent interviews Welch has granted to The Washington Post and The Associated Press.

In seeking to have the trial moved elsewhere, Rosen had argued that "everything about Mr. Welch from the time he was born until now" had been exposed to potential jurors here.

But Assistant U.S. Attorney Alexia Morrison, the chief government prosecutor in the case, argued that press accounts have been no more than straightforward reporting of the facts of the case, while Welch "endangered his own publicity" by granting the interviews.

Rosen's request that the trial be delayed in the wake of the Reagan assassination attempt stemmed from his assertion that public outrage at the attempt on the president's life, coupled with the fact that a cheap "Saturday night special" handgun allegedly was used in both the Halberstam and Reagan shootings, would prejudice jurors against his client.

But Moultrie denied the motion, saying that while there may be an "[abti]gun climate" becuase of the Reagan shooting, he was "faced with the problem of whether or not a day or 60 days or 10 years will eradicate the reaction from the public where guns are used." He said there is no assurance that a delay in the start of the trial would remove any possible animosity toward Welch.

Welch sat quietly in a powder-blue suit and open-necked white shirt as Moultrie then began the lengthly process of choosing a jury to hear the murder, robbery and burglary charges pending against Welch.

Afternoon recess, the judge began interviewing prospective jurors from a 97-member panel. He first asked if any of the panel members knew Halberstam, Welch or any of the attorneys. Three persons said they had known Halberstam and one woman said she knew Rosen. All were later excused from the jury.

Moultrie then began to interview each of the prospective jurors individually behind closed doors in his chambers -- a process that was only half completed by the end of the afternoon session.